1. Field of Invention
The present invention relates to a liquid crystal display. More particularly, the present invention relates to a transflective LCD.
2. Description of Related Art
To match the life style of modern people, video or imaging equipment is becoming lighter and slimmer. Although the conventional cathode ray tube (CRT) has many advantages, the design of the electron gun renders it heavy and bulky. Moreover, there is always some risk of hurting viewer's eyes due to the production of some harmful radiation. With big leaps in the techniques in manufacturing semiconductor devices and opto-electronic devices, flat panel displays such as liquid crystal displays (LCD), organic light-emitting displays (OLED) and plasma display panels (PDP) has gradually become the mainstream display products. According to the light source used, a liquid crystal display can be classified into three types: reflective LCD, transmissive LCD and transflective LCD. Taking a transflective LCD as an example, the transflective LCD mainly includes a transflective liquid crystal panel and a backlight unit. The transflective LCD panel includes a thin film transistor array, a color filter and a liquid crystal layer sandwiched therebetween. The backlight unit provides a surface light source to illuminate the transflective LCD panel for displaying images. More specifically, the thin film transistor array includes a plurality of pixels, each pixel has a transmissive region and a reflective region respectively, and wherein the thickness of liquid crystal layer located above the transmissive region is often different from the thickness of liquid crystal layer located above the reflective region.
FIG. 1 schematically illustrates a cross-sectional view of a conventional liquid crystal display. Referring to FIG. 1, the conventional LCD 10 includes a transflective LCD panel 100, a backlight unit 102 disposed under the transflective LCD panel 100, a polarizer 104a disposed between the transflective LCD panel 100 and the backlight unit 102, a polarizer 104b disposed above the transflective LCD panel 100, and a quarter wave plate 106 disposed between the transflective LCD panel 100 and the polarizer 104a. The light is polarized to the desired phase by the polarizer 104a implemented between the backlight unit 102 and the transflective LCD panel 100.
As shown in FIG. 1, the conventional transflective LCD panel 100 includes a thin film transistor array substrate (TFT array substrate) 110, a color filter substrate 120 disposed above the TFT array substrate 110, and a liquid crystal layer 130 filled between the TFT array substrate 110 and the color filter substrate 120. As shown in FIG. 1, the TFT array substrate 110 includes a transparent substrate 112, a plurality of thin film transistors (TFT) 114, a plurality of scan lines (not shown), a plurality of data lines 116, and a plurality of pixel electrodes 118. The TFT 114, the scan lines, the data lines 116, and the pixel electrodes 118 are all arranged over the transparent substrate 112. The layout of the TFT 114, the scan lines, the data lines 116, and the pixel electrodes 118 should be known by the ordinary skilled artisans, and are not described in detail. Each TFT 114 includes a gate electrode 114G electrically connected to the corresponding scan line, a source electrode 114S electrically connected to the corresponding data line 116, a drain electrode 114D electrically connected to the corresponding pixel electrode 118, and a channel layer 114C capable of turning on or off by a bias (e.g. Vgh or Vgl) that is applied to the gate electrode 114G.
As shown in FIG. 1, the pixel electrodes 118 includes a transparent electrode 118T and a reflective electrode 118R electrically connected to each other such that a plurality of transmissive regions T and reflective regions R of the transflective LCD panel 100 are defined. In detail, the transparent electrodes 118T permit light emitted from the backlight unit 102 passing through, and the reflective electrodes 118R reflect ambient light. Generally, the transparent electrodes 118T are made of indium tin oxide (ITO), indium zinc oxide (IZO), or other transparent conductive materials; the reflective electrodes 118R are made of metals or other reflective conductive materials.
Still referring to FIG. 1, the color filter substrate 120 includes a transparent substrate 122, a plurality of color filters 124R, 124G, and 124B, and a common electrode 126, wherein the color filters 124R, 124G, and 124B are disposed over the substrate 122, and the common electrode 126 are disposed above the color filters 124R, 124G, and 124B. Usually, the common electrode 126 is made of ITO, IZO, or other transparent conductive materials.
In the conventional LCD 10 described above, a portion of light provided by the backlight unit 102 is reflected back by the reflective electrodes 118R on the TFT array substrate 110; the other portion of light provided by the backlight unit 102 passes through the transparent electrodes 118T. In detail, the light reflected back by the reflective electrodes 118R is cut by the quarter wave plate 106 above the backlight unit 102. Therefore, the light reflected back by the reflective electrodes 118R can not be recycled. In addition, the manufacturing time and costs can not be reduced significantly because the polarizer 104a, the analyzer 104b and the quarter wave plate 106 are necessary for image displaying.